(i) Field of the Invention
This invention pertains to a method for shutting off or reducing the unwanted production of water from wells in a gas and oil-bearing formation due to flow through paths of least resistance.
(ii) Description of the Related Art
In the operation of wells used in the recovery of gases and associated liquids from subterranean formations unwanted passage of water can severely disrupt or in fact terminate the desired operation of a well. Frequently, a hydrocarbon reservoir contains water, either due to indigenous water or injected water. Water bypassing is often observed since the mobility of the water is usually high and therefore, when a pressure gradient is imposed, water tends to flow more readily than the hydrocarbon phases. The effects of water production are deleterious, as the water must be separated from saleable hydrocarbon products and disposed of in an environmentally safe manner. This can result in the well being shut in because of the adverse economics of increased separation and disposal costs of water compared to the declining hydrocarbons as water flow increases. In addition, the produced water can kill the gas flow in the well when the hydrostatic pressure of the water column is greater than the reservoir pressure (which prevents gas or oil flow). Artificial lifting costs to handle the water can add substantially to the cost of production.
These problems are not unique and the solutions have traditionally involved apparatus, methods, and compositions adapted to cover, seal or otherwise plug the openings thereby shutting off or reducing the passage of water. A barrier often is considered for unwanted liquid and gas production mitigation. There are a number of articles and patents describing various techniques which have been used to reduce water production due to coning or bottom water flow. Examples of these are Karp. Et al., Horizontal Barrier for Controlling Water Coning, Journal of Petroleum Technology, Vol. XX, pp. 783-790, 1962, Canadian Patent No. 1,277,936 to Costerton et al. and U.S. Pat. No. 5,062,483 issued to Kisman and Russell. These patents and the article discuss specific methods for isolation of bottom water flow. Polymers, such as polyacrylamide and polyphenolic resins, have been used in the past to enter the water conduits in the reservoir, and at a predefined time, setup or solidify to block or substantially impede water flow in the conduits. Since these solutions are aqueous they have a preference for the water conduits because of the low interfacial tension between two aqueous fluids. This can result in the aqueous solutions mixing with the large volumes of water and becoming unduly diluted.
These treatments have been successfully used for plugging high water flow regions but, due to their density, many times these treatments are gravimetrically unstable and are therefore less effective for bottom water control. Some of these previous applications are described in U.S. Pat. No. 4,683,949; U.S. Pat. No. 5,358,043; U.S. Pat. No. 5,418,217; U.S. Pat. No. 4,744,418; U.S. Pat. No. 5,338,465; U.S. Pat. No. 4,844,168 and U.S. Pat. No. 3,884,861.
Another technique disclosed in U.K. Patent GB 2,062,070A proposed a viscosified polymer which would be emulsified in oil and injected into a gas-producing formation to control bottom water production. This, however, was not successful due to the fact that the inherently high viscosity precluded the polymer from entering into many of the zones in which the water was flowing. Also, polymer gel emulsified in oil and stabilized with surfactants often suffer from phase separation in porous media.